clang  6.0.0svn
RangedConstraintManager.cpp
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1 //== RangedConstraintManager.cpp --------------------------------*- C++ -*--==//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines RangedConstraintManager, a class that provides a
11 // range-based constraint manager interface.
12 //
13 //===----------------------------------------------------------------------===//
14 
17 
18 namespace clang {
19 
20 namespace ento {
21 
23 
25  SymbolRef Sym,
26  bool Assumption) {
27  // Handle SymbolData.
28  if (isa<SymbolData>(Sym)) {
29  return assumeSymUnsupported(State, Sym, Assumption);
30 
31  // Handle symbolic expression.
32  } else if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(Sym)) {
33  // We can only simplify expressions whose RHS is an integer.
34 
35  BinaryOperator::Opcode op = SIE->getOpcode();
37  if (!Assumption)
39 
40  return assumeSymRel(State, SIE->getLHS(), op, SIE->getRHS());
41  }
42 
43  } else if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(Sym)) {
44  // Translate "a != b" to "(b - a) != 0".
45  // We invert the order of the operands as a heuristic for how loop
46  // conditions are usually written ("begin != end") as compared to length
47  // calculations ("end - begin"). The more correct thing to do would be to
48  // canonicalize "a - b" and "b - a", which would allow us to treat
49  // "a != b" and "b != a" the same.
50  SymbolManager &SymMgr = getSymbolManager();
51  BinaryOperator::Opcode Op = SSE->getOpcode();
53 
54  // For now, we only support comparing pointers.
55  assert(Loc::isLocType(SSE->getLHS()->getType()));
56  assert(Loc::isLocType(SSE->getRHS()->getType()));
57  QualType DiffTy = SymMgr.getContext().getPointerDiffType();
58  SymbolRef Subtraction =
59  SymMgr.getSymSymExpr(SSE->getRHS(), BO_Sub, SSE->getLHS(), DiffTy);
60 
61  const llvm::APSInt &Zero = getBasicVals().getValue(0, DiffTy);
63  if (!Assumption)
65  return assumeSymRel(State, Subtraction, Op, Zero);
66  }
67 
68  // If we get here, there's nothing else we can do but treat the symbol as
69  // opaque.
70  return assumeSymUnsupported(State, Sym, Assumption);
71 }
72 
74  ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From,
75  const llvm::APSInt &To, bool InRange) {
76  // Get the type used for calculating wraparound.
78  APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
79 
80  llvm::APSInt Adjustment = WraparoundType.getZeroValue();
81  SymbolRef AdjustedSym = Sym;
82  computeAdjustment(AdjustedSym, Adjustment);
83 
84  // Convert the right-hand side integer as necessary.
85  APSIntType ComparisonType = std::max(WraparoundType, APSIntType(From));
86  llvm::APSInt ConvertedFrom = ComparisonType.convert(From);
87  llvm::APSInt ConvertedTo = ComparisonType.convert(To);
88 
89  // Prefer unsigned comparisons.
90  if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
91  ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
92  Adjustment.setIsSigned(false);
93 
94  if (InRange)
95  return assumeSymWithinInclusiveRange(State, AdjustedSym, ConvertedFrom,
96  ConvertedTo, Adjustment);
97  return assumeSymOutsideInclusiveRange(State, AdjustedSym, ConvertedFrom,
98  ConvertedTo, Adjustment);
99 }
100 
103  SymbolRef Sym, bool Assumption) {
105  QualType T = Sym->getType();
106 
107  // Non-integer types are not supported.
108  if (!T->isIntegralOrEnumerationType())
109  return State;
110 
111  // Reverse the operation and add directly to state.
112  const llvm::APSInt &Zero = BVF.getValue(0, T);
113  if (Assumption)
114  return assumeSymNE(State, Sym, Zero, Zero);
115  else
116  return assumeSymEQ(State, Sym, Zero, Zero);
117 }
118 
120  SymbolRef Sym,
122  const llvm::APSInt &Int) {
123  assert(BinaryOperator::isComparisonOp(Op) &&
124  "Non-comparison ops should be rewritten as comparisons to zero.");
125 
126  // Simplification: translate an assume of a constraint of the form
127  // "(exp comparison_op expr) != 0" to true into an assume of
128  // "exp comparison_op expr" to true. (And similarly, an assume of the form
129  // "(exp comparison_op expr) == 0" to true into an assume of
130  // "exp comparison_op expr" to false.)
131  if (Int == 0 && (Op == BO_EQ || Op == BO_NE)) {
132  if (const BinarySymExpr *SE = dyn_cast<BinarySymExpr>(Sym))
133  if (BinaryOperator::isComparisonOp(SE->getOpcode()))
134  return assumeSym(State, Sym, (Op == BO_NE ? true : false));
135  }
136 
137  // Get the type used for calculating wraparound.
139  APSIntType WraparoundType = BVF.getAPSIntType(Sym->getType());
140 
141  // We only handle simple comparisons of the form "$sym == constant"
142  // or "($sym+constant1) == constant2".
143  // The adjustment is "constant1" in the above expression. It's used to
144  // "slide" the solution range around for modular arithmetic. For example,
145  // x < 4 has the solution [0, 3]. x+2 < 4 has the solution [0-2, 3-2], which
146  // in modular arithmetic is [0, 1] U [UINT_MAX-1, UINT_MAX]. It's up to
147  // the subclasses of SimpleConstraintManager to handle the adjustment.
148  llvm::APSInt Adjustment = WraparoundType.getZeroValue();
149  computeAdjustment(Sym, Adjustment);
150 
151  // Convert the right-hand side integer as necessary.
152  APSIntType ComparisonType = std::max(WraparoundType, APSIntType(Int));
153  llvm::APSInt ConvertedInt = ComparisonType.convert(Int);
154 
155  // Prefer unsigned comparisons.
156  if (ComparisonType.getBitWidth() == WraparoundType.getBitWidth() &&
157  ComparisonType.isUnsigned() && !WraparoundType.isUnsigned())
158  Adjustment.setIsSigned(false);
159 
160  switch (Op) {
161  default:
162  llvm_unreachable("invalid operation not caught by assertion above");
163 
164  case BO_EQ:
165  return assumeSymEQ(State, Sym, ConvertedInt, Adjustment);
166 
167  case BO_NE:
168  return assumeSymNE(State, Sym, ConvertedInt, Adjustment);
169 
170  case BO_GT:
171  return assumeSymGT(State, Sym, ConvertedInt, Adjustment);
172 
173  case BO_GE:
174  return assumeSymGE(State, Sym, ConvertedInt, Adjustment);
175 
176  case BO_LT:
177  return assumeSymLT(State, Sym, ConvertedInt, Adjustment);
178 
179  case BO_LE:
180  return assumeSymLE(State, Sym, ConvertedInt, Adjustment);
181  } // end switch
182 }
183 
184 void RangedConstraintManager::computeAdjustment(SymbolRef &Sym,
185  llvm::APSInt &Adjustment) {
186  // Is it a "($sym+constant1)" expression?
187  if (const SymIntExpr *SE = dyn_cast<SymIntExpr>(Sym)) {
188  BinaryOperator::Opcode Op = SE->getOpcode();
189  if (Op == BO_Add || Op == BO_Sub) {
190  Sym = SE->getLHS();
191  Adjustment = APSIntType(Adjustment).convert(SE->getRHS());
192 
193  // Don't forget to negate the adjustment if it's being subtracted.
194  // This should happen /after/ promotion, in case the value being
195  // subtracted is, say, CHAR_MIN, and the promoted type is 'int'.
196  if (Op == BO_Sub)
197  Adjustment = -Adjustment;
198  }
199  }
200 }
201 
202 } // end of namespace ento
203 
204 } // end of namespace clang
A (possibly-)qualified type.
Definition: Type.h:614
QualType getPointerDiffType() const
Return the unique type for "ptrdiff_t" (C99 7.17) defined in <stddef.h>.
ProgramStateRef assumeSym(ProgramStateRef State, SymbolRef Sym, bool Assumption) override
Given a symbolic expression that can be reasoned about, assume that it is true/false and generate the...
virtual ProgramStateRef assumeSymEQ(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &V, const llvm::APSInt &Adjustment)=0
virtual ProgramStateRef assumeSymLE(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &V, const llvm::APSInt &Adjustment)=0
Symbolic value.
Definition: SymExpr.h:29
virtual ProgramStateRef assumeSymLT(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &V, const llvm::APSInt &Adjustment)=0
static Opcode reverseComparisonOp(Opcode Opc)
Definition: Expr.h:3092
LineState State
bool isIntegralOrEnumerationType() const
Determine whether this type is an integral or enumeration type.
Definition: Type.h:6013
static bool isLocType(QualType T)
Definition: SVals.h:307
BinaryOperatorKind
A record of the "type" of an APSInt, used for conversions.
Definition: APSIntType.h:20
Represents a symbolic expression like &#39;x&#39; + 3.
llvm::APSInt getZeroValue() const LLVM_READONLY
Returns an all-zero value for this type.
Definition: APSIntType.h:56
virtual QualType getType() const =0
static Opcode negateComparisonOp(Opcode Opc)
Definition: Expr.h:3079
ProgramStateRef assumeSymUnsupported(ProgramStateRef State, SymbolRef Sym, bool Assumption) override
Given a symbolic expression that cannot be reasoned about, assume that it is zero/nonzero and add it ...
BasicValueFactory & getBasicVals() const
const FunctionProtoType * T
uint32_t getBitWidth() const
Definition: APSIntType.h:31
bool isComparisonOp() const
Definition: Expr.h:3077
const SymSymExpr * getSymSymExpr(const SymExpr *lhs, BinaryOperator::Opcode op, const SymExpr *rhs, QualType t)
virtual ProgramStateRef assumeSymRel(ProgramStateRef State, SymbolRef Sym, BinaryOperator::Opcode op, const llvm::APSInt &Int)
Assume a constraint between a symbolic expression and a concrete integer.
virtual ProgramStateRef assumeSymOutsideInclusiveRange(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From, const llvm::APSInt &To, const llvm::APSInt &Adjustment)=0
llvm::APSInt convert(const llvm::APSInt &Value) const LLVM_READONLY
Convert and return a new APSInt with the given value, but this type&#39;s bit width and signedness...
Definition: APSIntType.h:49
Dataflow Directional Tag Classes.
virtual ProgramStateRef assumeSymGT(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &V, const llvm::APSInt &Adjustment)=0
Represents a symbolic expression involving a binary operator.
virtual ProgramStateRef assumeSymNE(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &V, const llvm::APSInt &Adjustment)=0
APSIntType getAPSIntType(QualType T) const
Returns the type of the APSInt used to store values of the given QualType.
bool isUnsigned() const
Definition: APSIntType.h:32
ProgramStateRef assumeSymInclusiveRange(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From, const llvm::APSInt &To, bool InRange) override
Given a symbolic expression within the range [From, To], assume that it is true/false and generate th...
virtual ProgramStateRef assumeSymWithinInclusiveRange(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &From, const llvm::APSInt &To, const llvm::APSInt &Adjustment)=0
char __ovld __cnfn max(char x, char y)
Returns y if x < y, otherwise it returns x.
Represents a symbolic expression like &#39;x&#39; + &#39;y&#39;.
virtual ProgramStateRef assumeSymGE(ProgramStateRef State, SymbolRef Sym, const llvm::APSInt &V, const llvm::APSInt &Adjustment)=0